Filter device, and filtration and cleaning method

ABSTRACT

The present invention relates to a filter device for completely removing residual amounts, after filtration, from the space of the unfiltered product. The filter device comprises a plurality of parallel filtration plates which are separated by filtration layers as well as by membrane plates submitted to the action of pressurized air. The membrane plates are exclusively covered on both sides by a stretched membrane, wherein said membranes have a smooth outer surface and are made of a flexible material so as to cover completely the adjacent space of the unfiltered product.

This application is a 371 of PCT/EP99/08708, filed Nov. 11, 1999 andclaims the benefit of Germany application 198 52 084.0, filed Nov. 12,1998.

FIELD OF THE INVENTION

The invention relates to a device for the continuous filtration offluids by means of the pressure differential between the inlet andoutlet, as well as the removal of residual amounts of the slurry bymeans of a pneumatic pressure medium before opening the device, saiddevice having

a plurality of filter plates having a slot on both sides for seating aplanar filter medium and equipped with drainage channels for thefiltrate;

a plurality of membrane plates having connections, bores and recessesfor the admission of the pressure medium, which membrane plates arecovered on both sides with an elastic membrane such that a slurrychamber or a filter cake chamber is formed between the filter medium andthe membrane;

corresponding recesses in the filter plates and membrane plates whichwhen installed form at least one admission channel for the slurry andone drainage channel for the filtrate, and also having

end plates, retaining fixtures and clamping fixtures to connect thefilter plates, membrane plates and frames to form a filter pack that canlater be disassembled.

The invention also relates to a filtration and cleaning method. From theaspect of its structural design, such a device belongs to the group ofdevices known as filter presses. However, it is used for filtration likea plate filter, in which the filtrate is forced through the filtermedium by means of the pressure differential of the fluid between theinlet and the outlet.

BACKGROUND OF THE INVENTION

A prior art example of a plate filter is disclosed in DE 39 06 816 C3.There are a plurality of filter plates arranged in parallel consolidatedinto a filter pack. When assembled, filter beds is pressed togetherbetween mating surfaces of the filter plates, which provide a sealbetween the slurry chambers and the filtrate chambers, and seal theentire filter pack to the outside.

A prior art example of a filter press is disclosed in DE 39 32 422 A1.The membrane plates alternately disposed between the usual filter platescomprise a circular frame with connections for the admission anddrainage of a pressure medium, and a central wall, with a membraneattached to each side of a frame symmetrical to the central wall via aclamping ring. The axial length of the filter press is due to thecumulative width of the filter plates and the frame elements of themembrane plates. The space between the central wall of the membraneplate and the filter media attached to both sides of the filter platesis divided by the membranes into roughly equal sized suspension andpressure medium chambers. The frame elements have bead-like elevationsextending along the axis of the filter device, over which elevations themembranes are stretched to improve their durability/stability whensubjected to cyclic loads of up to 120 bar in these particularlycritical areas. Because the membrane is stretched and arranged in thismanner, the membrane is not extended but compressed when impinged by thepressure medium during the press process. As a result, the membranenever makes complete contact with the membrane plate when unpressurized,nor can the membrane make complete contact and lie flat against thefilter plate when pressurized. Given the purpose of the generic device,the prior art filter press has an unnecessarily long axial length due tothe pressure media chambers between the membranes and the central wallsof the membrane plates. In other words, the space between the filterplate and the membrane plate that can be used as a slurry chamber isquasi halved because of the central position of the membranes, whichunder otherwise identical conditions also results in an oversized filterpress.

The prior art also discloses filter devices in which pressurizedmembranes work in conjunction with filter cloths that must completely orpartially match the change in shape of the membranes during filtration.In these cases, the membranes are equipped on the side facing the filtercloth with spacing cams so that the filtrate passing through the filtercloth can drain between the filter cloth and the membrane. Suchmembranes are unsuited for the intended application of the deviceaccording to the current invention.

SUMMARY OF THE INVENTION

The object of the current invention is therefore to refine a prior artdevice as described above for the filtration of fluids such that theresidual losses can be significantly reduced compared to conventionalplate filters without having to accept the disadvantages of prior artfilter presses.

To achieve this object, the current invention teaches that the filtermedium comprises sections of a sheet filter material mounted in therecesses of the filter plates; that the membranes, which whenpressurized expand elastically to completely contact the filter platesor sheet filter material, have a smooth surface on both sides and makecomplete contact with the membrane plates when depressurized.

Sections of a proven and inexpensive sheet filter material can be usedas the filter medium because the normal filtration process is the sameas with conventional plate filters. Sheet filter material has alabyrinth-like depth filtration structure, which when used inconjunction with different surface charges permits both mechanical andadsorptive separation of particles along the relatively long paththrough the filtration medium. These materials, also known as filterbeds, are special paperboards for the filtration of fluid media with thegoal of removing coarse to super-fine particles, colloids,microorganisms and other undesirable components, and thus maintain thedesired quality of the filtrate or to extract solid residues. These aremanufactured using special paper machines, primarily Fourdrinier papermachines.

The raw materials are usually selected, bleached celluloses from coniferor deciduous woods of high purity, i.e. with high alpha content,selected diatomaceous earths and perlites, as well as manmade fiberssuch as polyolefin fibers, activated carbon, polyvinylpyrrolidone (PVP)or similar materials for special applications.

Most filter beds can be backed on the downstream side to prevent theloss of fibers during filtration without adversely affectingflowthrough. Certain approved resins can be used in small amounts toachieve specific effects (interfacial potentials, zeta potential).

The selection of raw materials, the processing thereof and the blendingratios together with other manufacturing parameters determineeffectiveness and application.

The alternately disposed membrane plates are only activated when forcingresidual amounts of the product from the slurry chamber prior to openingthe device, and the remaining filtrate is forced by means of thepressurized membranes through the filter cake and the filter medium.

Because the slurry chamber is completely lined by the membrane whenpressurized, it is possible to reduce the residual losses to nearly zerobecause the slurry chamber can be almost completely emptied by means ofthe membranes, and because the filter cakes are also mechanicallypressed. The filter cake is solidified and nearly completely free ofresidual filtrate. The filter cake is almost completely dry and can beeasily removed together with the filter medium after opening the filterdevice. The filter cake is thus prepared for further processing as isrequired in some filtration applications, such as the separation ofblood plasma, for example.

A membrane that is smooth on both sides prevents filter cakeconstituents from sticking to the membrane, and also ensures that thedrainage channels in the filter plates can be optimally covered whenimpinged with a fast-flowing detergent for cleaning.

The drainage channels on the filter plate are preferably vertical andhorizontal grooves in the filter plate in the area of the groove for thesections of the sheet filter material.

The drainage channels on the filter plate are preferably vertical andhorizontal grooves formed in the area of the slot in the filter platesfor the sections of sheet filter material.

The horizontal and/or vertical grooves are preferably connected to atleast one filtrate manifold in the interior of the filter plate.

At least one frame is located between each membrane plate and the filterbed to define and adjust as necessary the size of the slurry chamber.This makes it possible to adapt the size of the slurry chamber to thefiltration job, in particular when the thickness of the filter cake isnot the same for all filtration processes.

The frames can be polygonal, preferably square, and enclose bothhorizontally and vertically a slurry or filter cake chamber having atrapezoidal cross-section, whereby the boundary surface formed by themembrane plate is larger than the boundary surface formed by theopposing filter plate.

It is advantageous for the frame to have beveled inner surfaces tofacilitate the expansion and contacting of the membranes when inflated.The bevel is preferably such that the frame thickness continuouslydecreases from the membrane side to the filter bed side. This preventsdead spaces because the inflated membrane can completely line the slurrychamber.

The membrane plate is preferably equipped with a support body on whichthe membrane is arranged. A compressed air duct is preferably located inthe support body, which duct is connected via outlet openings to the twosurfaces of the support body adjacent to the membranes. The compressedair duct is preferably branched. The recesses for the inlet and drainagechannels in the filter plates are preferably in the area of the slotsfor the sections of sheet filter material.

The sections of sheet filter material can preferably be pressed togetheredge-to-edge between the filter plates and the frames to form a seal.The sections of sheet filter material are used to form a seal betweenthe chambers containing the slurry and the filtrate, as well as to sealthe device to the outside. The advantage of this is that additional sealelements are not required.

The measure also helps ensure that the membranes extend over the entiresurface of the membrane plates and when installed are clamped togetheredge-to-edge between the membrane plates and the frames to form a seal.

The membranes preferably protrude over the uniform contour of the filterplates at least in the area of the connections for the pneumaticpressure medium. This configuration offers the advantage that thefasteners for the membranes are accessible from outside the device.

The compressed air connections of the membrane plates are located on theend face of the membrane plates, preferably outside of the vertical,longitudinal midplane of the device. This significantly aids side accessto the compressed air connections by operating personnel duringinstallation.

The filter plates can have a groove running around the outside on bothsides at some distance from the edge for seating a seal, which seal canbe considered a supplemental measure given the seal function alreadyprovided.

The filter plates, membrane plates and/or the frames are made primarilyof plastic, preferably polypropylene or polypropylene copolymers so thatFDA listing can be attained and the device can be used for thefiltration of sensitive fluids. The filter device is thereforeparticularly suited for blood filtration.

The membrane is preferably made of a thermoplastic elastomer. Theadvantage of this material that it is very highly flexible, enabling themembrane to completely contact the contour of the slurry chamber.

The method for filtering fluids using the device teaches that actualfiltration is by means of the pressure differential of the fluid betweenthe inlet and the outlet, and that the membrane plate is impinged by apressure medium, pressing the membranes against the filter cakes, filtermedia and filter plates to press out residual amounts of slurry and todry and solidify the filter cake.

The method for cleaning the device teaches that the filter plates,membrane plates and possibly the frames without sections of sheet filtermaterial are first assembled, the membranes are inflated untilcontacting or nearly contacting the filter plates, and finally afast-flowing cleaning fluid is sent through the filtrate drainagechannels in the filter plates.

It is possible to only inflate the membrane far enough to create a smallspace between the membrane and the filter plate with a correspondinglysmall cross-section so that high velocity cleaning fluid flows can beachieved. The flow velocity of 2 m/s required for optimal cleaning canbe easily achieved.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 a perspective view of the filter device;

FIGS. 2a, b a side view, partly in section, of the filter arrangement,with inflated and uninflated membranes;

FIGS. 3a-c top views and partial sections of the membrane plate;

FIGS. 4a-c top views and partial sections of the frame;

FIGS. 5a-d top views and partial sections of a filter plate.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a perspective view of a filter device 1. The filter device hasa moveable frame 2 with a frame plate 3 a, b on each end, which frameplates are connected together by means of two side rails 4. The filterplates 40, frames 20 and membrane plates 30 are hung from these siderails 4 to form a plate arrangement 9 and pressed together by means of apressing device to form a seal. The membrane plates 30 have compressedair connections 7′ to which hoses 7 are connected, which hoses are runover a bar 8 to a common compressed air supply (not shown).

Connections 5 and 6 for the filtrate inlet and filtrate outlet areprovided at the front of the frame 2 and are connected to the filtrateand slurry channels within the plates 30, 40 and the frames 20.Appropriately dimensioned eyes are provided in the corners of the plates30, 40 and the frames 20 to form these filtrate and slurry channels.

A filter plate arrangement 9 is shown in detail in FIG. 2a. Loose covers12 a, 12 b are located at both ends of the complete arrangement, whichcovers exert pressure against the plates and frames arranged between thecovers via a suitable thruster. Immediately adjacent to the two loosecovers are the end plates 10 a and 10 b. Then comes a frame 20, amembrane plate 30, another frame 20 and a filter plate 40. Thisarrangement is then repeated any number of times. All frames and plateshave support lugs 11, 21, 31, 41 by means of which they are supportedfor movement on the side rail 4.

The middle section is a sectional view of the individual plates, whichare described in detail with reference to the remaining figures. Theframe 20 essentially comprises a rectangular or square frame, which isin tight contact with the adjacent membrane plate 30 or membrane 33 a, band the filter plate 40 or filter bed 50. The frame 20, together withthe adjacent filter bed 50 and the membrane 33 a, b, delimits the slurrychamber 26. The filter plate 40 comprises a solid plastic componenthaving horizontal and vertical grooves on the side surfaces. The filterbeds 50 are inserted into corresponding slots.

The membrane plate 30 always protrudes above the other components andhas a support body 32, on both sides of which there is a membrane 33 a,b. The membranes 33 a, b can be inflated via a compressed air duct 34 sothat they extend into and completely line the slurry chamber 26, as isshown in FIG. 2b. The filter cake that forms during filtration is notshown so that the membrane 33 a, b is in direct contact with the filterbed 50.

Such a membrane plate 30 is shown in detail in FIG. 3a. The support body32 of the membrane plate 30 has a rectangular or square contour and lugs31 on the sides by means of which the membrane plate is supported on theside rail 4. The compressed air connection 7′ located off-center on thetop of the plate is in communication with a compressed air duct 34 inthe interior, which duct has two branches 35 a and b. In the embodimentshown here, the branches form a Y.

As can be seen in FIG. 3b, each compressed air duct 34 or correspondingbranches 35 a and b extend through the center of the support body 32 ofthe membrane plate 30 and is equipped with outlet openings 36 a, b thatend at both surfaces of the support body 32, thus forming a connectionto the two grooves 37 in the surface of the support body 32. The grooves37 improve the distribution of air below the membrane 33 a, b so thatthe membranes 33 a and b can be easily inflated.

FIG. 3c shows how the membranes 33 a, b are bolted by means of the twobolts 39 a, b. The eyes 38 a-d, together with the eyes in the othercomponents, form channels for the filtrate and the slurry.

FIG. 4a shows a frame 20 also having four eyes 25 a-d at the samelocations. Frame 20 also has support lugs 21 that rest on the side rails4. As is shown in Sections A—A and B—B in FIGS. 4b and 4 c,respectively, the inner surfaces 22 are beveled. The bevel is from thefilter bed side 24 toward the membrane plate 30 (membrane side 23) sothat the membrane 33 a, b can more easily lie against the contour of theframe 20 and thus the contour of the slurry chamber 26 when inflated.

FIG. 5a shows a top view of a filter plate 40 without the filter bed 50.This plate also has corresponding eyes 46 a-d and support lugs 41. Aslot 45 a, b runs around each edge for seating a round cord as a seal.

In that area where the filter bed 50 is applied the filter plate 40 hasa corresponding slot 42 a/42 b on each side, which slot also encompassesthe area with the eyes 44 a-d because the filter bed also has eyes atthe corresponding locations. The depth of the slot 42 a, b is roughlyequal to the thickness of the filter bed 50 to be inserted. Located inthis area are both horizontal grooves 44 a, b and vertical grooves 43 a,b, which enable the filtrate beneath the filter bed 50 to drain (cf.FIGS. 5a-d). The horizontal grooves 44 a, b are each arranged in anupper and lower strip-like area and provide lateral distribution of thefiltrate. The filtrate is collected in a laterally running filtratechannel 48, which is connected via connecting openings 49 to the groovesin the lower section of the filter plate 40. This manifold 48 isconnected to the eye 46 c. The upper eye 46 d is connected to acorresponding duct arrangement for the supply of air.

An enlarged view of the vertical and horizontal grooves is shown in FIG.5d, in which the detail X is enlarged. The outer vertical groove 43 abecomes a diagonal groove 47 in the area of the eye 46 c.

REFERENCE NUMBERS

1 Filter device

2 Frame

3 a, b Frame plate

4 Side rail

5 Filtrate inlet

6 Filtrate outlet

7 Compressed air hose

7′ Compressed air connection

8 Bar

9 Plate arrangement

10 a, b End plate

11 Support lug

12 a, b Cover

20 Frame

21 Support lug

22 Inner surface

23 Membrane side

24 Filter bed side

25 a-d Eye

26 Slurry chamber

30 Membrane plate

31 Support lug

32 Support body

33 a, b Membrane

34 Compressed air duct

35 a, b Duct branch

36 a, b Outlet opening

37 Groove

38 a,b,c,d Eye

39 a, b Bolt

40 Filter plate

41 Support lug

42 a,b Slot

43 a,b Vertical groove

44 a,b Horizontal groove

45 a,b Slot for round cord

46 a-d Eye

47 Diagonal groove

48 Manifold

49 Connecting opening

50 Filter bed, section of sheet filter material

What is claimed is:
 1. A device for the continuous filtration of fluidsby means of a pressure differential between the inlet and outlet, aswell as the removal of residual amounts of the slurry by means of apneumatic pressure medium before opening the device, said devicecomprising: a plurality of filter plates having a slot on both sides forseating a planar filter medium and equipped with drainage channels forthe filtrate; a plurality of membrane plates having connections, boresand recesses for the admission of the pressure medium, which membraneplates are covered on both sides with an elastic membrane such that aslurry chamber or a filter cake chamber is formed between the filtermedium and the membrane, whereby the membranes, which when pressurizedexpand elastically to completely contact the filter plates or sheetfilter material, have a smooth surface on both sides and make completecontact with the membrane plate when depressurized; frames between themembrane plates and the filter plates which delimit the slurry chamber,corresponding recesses in the filter plates and membrane plates whichwhen installed form at least one admission channel for the slurry andone drainage channel for the filtrate, and end plates, retainingfixtures and clamping fixtures to connect the filter plates and membraneplates to form a filter pack that can later be disassembled, wherein thefilter medium comprises sections of a sheet filter material mounted inthe slots, and that sections of sheet filter material can be pressedtogether edge-to-edge between the filter plates and the frames to form aseal.
 2. A device as claimed in claim 1, wherein the drainage channelscomprise vertical grooves and horizontal grooves, and are formed in thefilter plates in the area of the slots for the sheet filter material. 3.A device as claimed in claim 2, wherein the grooves are connected to atleast one filtrate manifold inside the filter plate.
 4. A device asclaimed in claim 1, wherein the frames are rectangular, and enclose bothhorizontally and vertically a slurry or filter cake chamber having atrapezoidal cross-section, whereby the boundary surface formed by themembrane plate is larger than the opposing boundary surface formed bythe filter plate.
 5. A device as claimed in claim 1, wherein themembrane plate has a support body on which the membranes are arrangedand wherein there is a compressed air duct in the support body, saidduct connected via outlet openings to the two surfaces of the supportbody adjacent to the membranes.
 6. A device as claimed in claim 1,wherein the recesses for the inlet and drainage channels in the filterplates are in the area of the slots for the sections of sheet filtermaterial.
 7. A device as claimed in claim 1, wherein the sections ofsheet filter material are used to provide a seal between the slurrychambers and the filtrate chambers, and to seal the device to theoutside.
 8. A device as claimed in claim 1, wherein the membranes extendover the entire surface of the membrane plates and when installed areclamped together edge-to-edge between the membrane plates and the framesto form a seal.
 9. A device as claimed in claim 1, wherein the membraneplates protrude over the uniform contour of the filter plates at leastin the area of the connections for the pneumatic pressure medium.
 10. Adevice as claimed in claim 9, wherein the connections an the end of themembrane plates are preferably located outside of the vertical,longitudinal midplane of the device.
 11. A device as claimed in claim 1wherein the filter plates have a groove running around the outside onboth sides at some distance from the edge for seating a seal.
 12. Adevice as claimed in claim 1, wherein the membranes are of athermoplastic elastomer.
 13. A device as claimed in claim 1, wherein thefilter plates, the membrane plates and/or the frames are of plastic. 14.A device as claimed in claim 1, wherein the frames are square, andenclose both horizontally and vertically a slurry or filter cake chamberhaving a trapezoidal cross-section, whereby the boundary surface formedby the membrane plate is larger than the opposing boundary surfaceformed by the filter plate.
 15. The device of claim 1, wherein thefluids comprise blood.